Methods and mechanisms for thermal semi conduction

ABSTRACT

Thermal semi conductor is a mechanism for the control of conduction heat flux between two or more bodies with differing temperatures, promoting the unidirectional heat flux. It consists of composite slabs composed of materials with high and low thermal conductivity appropriately set, granting the thermal semi conduction. These slabs are able to displace allowing the contact between materials with high thermal conductivity respectively in order to promote higher heat flux or, in opposite, to displace facilitating the contact between materials with low thermal conductivity respectively to promote lower heat flux. The control of the heat transfer through the mechanism is defined by positioning the slabs appropriately. External devices can be used to promote the relative displacement of the slabs. On the other hand, an adequate design of the slabs can be used to promote or to avoid their thermal contact through thermal expansion or contraction. In this case, the control of the process can be reached automatically by the temperature gradient.

BACKGROUND

1. Field of the Invention

The present invention, namely thermal semi conductor, relates to adevice for heat flux control, which promotes unidirectional conductionheat transfer. The thermal semi conductor can be employed in anysituation where a thermal insulator or a thermal conductor mightotherwise be employed. However, the thermal semi conductor is superiorto a thermal conductor/insulator in several aspects. The invention hasparticular utility in the promoting of the unidirectional heat transfer,improving the storage capacity of systems with time-dependent thermalenergy sources or sinks, etc.

2. State of the Art

Although the present invention is quite similar from systems withthermal conductors or insulators, thermal conductors or insulatorsnevertheless provide a convenient reference point for purposes ofcomparison. As is well known, in principle thermal insulators consist oflow thermal conductivity materials manufactured or combined in a way toachieve an even lower system thermal conductivity. Considering anunfavorable temperature gradient, this feature is useful to reduce therate of heat transfer preserving the temperature of rooms, objects,process fluids, etc, avoiding thermal losses. However, if thetemperature gradient is favorable, thermal insulators isolate the systempreventing substantial thermal gains in addition. In that situationhowever, the use of thermal conductors are attractive for the reasonthat they increase the system rate of heat transfer, promoting thermalgains. Thus, methods and processes to control the rate of heat transferto take advantage of the temperature gradient has been attempt. In thisway, thermal semi conductors are able to perform this purpose.

While thermal insulators and conductors have found wide application,they nevertheless have disadvantages in particular which are overcome bythe present invention. One disadvantage of conventional thermalinsulators and conductors systems is that they don't permit thetransient control of the heat flux. Systems subjected to intermittenttemperature gradient can take advantage of favorable temperaturegradient to increase their operational performance.

For instance, the objective of insulation traditionally used inbuildings is to retard heat transfer. Thermal insulation is installed inbuildings to provide thermal comfort and to reduce operating costsgenerated by heating, ventilation and air-conditioning. However,appropriate thermal semi conductors can be employed to maintain thebuilding environment at a desired temperature range throughout the sun'sdaily and annual cycles. As a result it generally minimizes the use ofactive solar, renewable energy and especially fossil fuel technologies.

Techniques for dissipation the heat generated by electronic devices andcircuitry includes heat sinks and fans for air cooling. Particularly, anactive region separated from the ventilated heat sink by a siliconsubstrate and a metal integrated heat spreader is the microprocessorheat transfer plate where heat exchange is achieved by conduction.Because of the localized heat source, the thermal spreading resistanceof the interface region can be high. Appropriate thermal semi conductorsconfigurations can alleviate on-chip hotspots much more effectively thanany type of heat spreader and also contribute to a better chiptemperature uniformity.

SUMMARY

Accordingly, it is an object of the invention to provide techniques andprocesses for the unidirectional heat transfer. For that, compositeslabs formed of materials with high and low thermal conductivity areappropriately set and adjusted permitting the thermal semi conduction.According to the proposed invention, the thermal semi conductionmechanism can be achieved by relative mechanical slabs positioning orautomatically by temperature gradient.

It is another object of the invention to provide such devices whosepermit the transient control of the heat flux.

BRIEF DESCRIPTION OF THE DRAWINGS

While the novel features of the invention are set forth withparticularity in the appended claims, the invention, both as toorganization and content, will be better understood and appreciated,along with other objects and features thereof, from the followingdetailed description, taken in conjunction with the drawings in which:

FIG. 1—Cross-sectional view of one form of thermal semi conductor devicebased on compound materials and thermal contact—minimal bulk thermalconductivity.

FIG. 2—Cross-sectional view of one form of thermal semi conductor devicebased on compound materials and thermal contact—intermediate bulkthermal conductivity.

FIG. 3—Cross-sectional view of one form of thermal semi conductor devicebased on compound materials and thermal contact—maximal bulk thermalconductivity.

FIG. 4—Cross-sectional view of one form of thermal semi conductor basedon compound materials and thermal contact between extendedsurfaces—minimal bulk thermal conductivity.

FIG. 5—Cross-sectional view of one form of thermal semi conductor basedon compound materials and thermal contact between extendedsurfaces—maximal bulk thermal conductivity.

FIG. 6—Cross-sectional view of one form of thermal semi conductor basedon compound materials and thermal contact between extendedsurfaces—intermediate bulk thermal conductivity.

FIG. 7—Cross-sectional view of one form of thermal semi conductor basedon compound materials, thermal contact between extended surfaces andthermal expansion/contraction—minimal bulk thermal conductivity.

FIG. 8—Cross-sectional view of one form of thermal semi conductor basedon compound materials, thermal contact between extended surfaces andthermal expansion/contraction—maximal bulk thermal conductivity.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In general, rate of heat transfer is proportional to the product ofthree factors: thermal conductivity, the area over which heat transferoccurs, and temperature gradient (temperature difference per unitdistance). Applying this general relationship to the invention, themagnitude of the thermal conductivity for the system depends on itsstructure. Usually, the bulk thermal conductivity is subject topredictable constraints. In the present invention, such a bulk thermalconductivity can be systematically modified by combining the thermalcontact effect with an adaptive structure consisting of materials withgood and poor thermal conductivity. The area factor is also subject topredictable constraints. Considering that the area over which heattransfer takes place remains unchanged, it does not influence the heattransfer rate. The third factor, temperature gradient, is anothermatter, not subject to constraints which are obvious.

A heat transfer device in accordance with the invention includes atleast a pair of slabs adapted for positioning at respective locationswith differing temperatures between which it is desired to control thedirection and the heat transfer rate. A basic configuration consists inan arrangement of slideable composite slabs formed of good conductormaterial and good insulator material intercalated, namely, a thermalsemi conductor device based on compound materials and thermal contact.The adequate displacement of these slabs permitting the contact betweengood thermal conductor materials respectively produces higher heatfluxes. On the contrary, the displacement of these slabs preventing thecontact between good thermal conductor materials respectively produceslower heat fluxes. The thermal conductivity of the system and,consequently, the heat flux can be controlled through an intermediatepositioning of the slabs.

As another configuration is a system comprising two slideable parallelsymmetric plates of a good conductor with internal extended surfaces,similar to fins, namely, the thermal semi conductor based on compoundmaterials and thermal contact between extended surfaces. The remainingspace is filled with a good insulator. Intentionally, a gap is leftbetween fins with corresponding apparent surfaces, allowing the relativelongitudinal displacement of the slabs. The longitudinal displacement ofthe plates works like an on-off switch promoting or preventing thethermal flux. By transversal dislocation, the thermal contact area canbe reduced or increased reducing or increasing, respectively, thethermal conductivity of the system modifying the heat flux through thewall.

The third configuration is similar to the previous one. This systemconsists of two parallel plates of a good conductor with internal fins.The fins of one wall are intentionally confined by fins of the otherwall. The remaining space is filled with a good insulator and a gap isleft between fins with corresponding apparent surfaces. In this proposedconfiguration, two right wall fins are confined by two left wall fins.By this way, higher temperatures at the left side of the wall promoteits thermal expansion. On the other hand, lower temperatures at theright side of the wall promote its thermal contraction. This conjugatedeffect keeps the corresponding fin surfaces apart from each otherenhancing, in this way, the thermal insulation between the left and theright regions. On the contrary, when higher temperatures occur at theleft side and lower temperatures occur at the right side, thermalcontraction and expansion takes place, respectively. Because of thisconjugated effect, the contact between the corresponding fin surfacestakes place increasing through that the capability of the system toconduct thermal energy. In opposite of the previous system, this systemis operated exclusively by defined temperature gradients and no externaldriven is necessary for its working. This system automatically switchesbetween good or poor thermal conductivity by corresponding temperaturegradients.

Thus, with the three presented configurations, large quantities of heatare transported unidirectionally by providing the adequate design andthe satisfactory slabs arrangement.

In any given configuration, there is a most adequate configuration ofthe slabs thickness and segments width regarding the desired maximum andminimum heat flux. Particularly, the third configuration requires anoptimum design concerning the temperature gradient between thereservoirs. If the gap is too large, then the thermal contact betweenthe materials with good thermal conductivity does not occur and thesystem becomes a good thermal insulator. If the gap is too small, thenthe materials with good thermal conductivity remain contacted and thesystem becomes a good thermal conductor.

It should be understood that the invention is not limited to thepresented configurations, and that various changes (parts, dimensions,shapes, geometries, materials, configurations, arrangements, etc.) maybe made by those skilled in the art without changing the essentialcharacteristics and the basic concepts of the invention.

As is known, the heat conduction between the slabs of a composite wallis strongly influenced by the contact resistance, especially ifhigh-conductivity metals are involved. The contact resistance isdependent on the pressure which contact in maintained. Somerepresentative data for contact resistances are presented by Mills(1995) and Hagen (1999). Good interfacial conductances can arrive ath_(i)=2.5×10⁴ W/m²·K for a copper-copper interface and h_(i)=4.0×10⁴W/m²·K for an iron-aluminum interface at moderate pressure and usualfinishes. As a first approach, the interfacial contact resistancebetween the slabs is neglected.

Finally, serial and/or parallel and/or form of matrices arrangements ofmultiple slabs can be used to achieve the desired heat flux control.

The following configurations are provided by way of illustration onlyand not by way of limitation. A variety of parameters can be changed ofmodified to yield essentially similar results and would be apparent toone skilled in the art.

Thermal Semi Conductor Based on Compound Materials and Thermal Contact

Referring first to FIG. 1, an exemplary thermal semi conductor device 1based on compound materials and thermal contact in accordance with theinvention includes a pair of slabs 2 and 3 assembled with a intercalatesequence of segments with equivalent length of a relatively good and apoor thermal conductor materials adapted for positioning at respectivelocations of differing temperature between which it is desired tocontrol the heat transfer. These slabs are maintained in contact butthey are, at the same time, able to slide vertically. By way of example,the reservoir C is a relatively colder reservoir and is positioned sothat to transfer heat from relatively hotter reservoir H. The slabs arepositioned, so that the slab segments with materials with good thermalconductivities 4 and with poor thermal conductivities 5 are aligned. Atthis positioning, the system has the minimal bulk thermal conductivityand heat transfer achieves the lowest rates.

By promoting the relative slabs longitudinal displacement as shownschematically in FIG. 2, segments with good heat conductivity 4 are setin contact and the bulk thermal conductivity of the system increases,increasing the heat transfer rate. The non-aligned slabs positioningallows a dynamic heat transfer control as desired. When the segmentswith higher thermal conductivity 4 are aligned, the bulk thermalconductivity of the system achieves its maximum value, as presented inFIG. 3.

Thermal Semi Conductor Based on Compound Materials and Thermal ContactBetween Extended Surfaces

FIG. 4 presents, an exemplary thermal semi conductor device 10 based oncompound materials and thermal contact between extended surfaces inaccordance with the invention. This design includes two internallyfinned slabs 8 of a material with good thermal conductivity filled witha material with poor thermal conductivity 7 adapted for positioning atrespective locations with differing temperature between which it isdesired to control the heat transfer. These slabs are maintained incontact but they are, at the same time, able to slide longitudinally andtransversally. By way of example, the reservoir C is a relatively colderreservoir and is positioned so that to transfer heat from relativelyhotter reservoir H. The gap 9 is filled with a compressible fluid withlow thermal conductivity. By keeping the internal fins 6 apart from eachother, the bulk thermal conductivity of the system is relatively lower.As shown in FIG. 5, when the slabs displace longitudinally and theinternal fins of material with good thermal conductivity are set incontact, the bulk thermal conductivity increases, allowing relativelyhigher heat fluxes. At this position, the system presents its maximalbulk heat conductivity. When the slabs displace transversally apart fromeach other keeping the contact between the internal fins, according toFIG. 6, the bulk thermal conductivity decreases to a relativelyintermediate value. Since the fluid inside the slabs is compressible,the slabs displacements in both transversal and longitudinally directionare guaranteed. This relative slabs displacement permits thus thecontrol of the heat transfer between the reservoirs.

Thermal Semi Conductor Based on Compound Materials, Thermal ContactBetween Extended Surfaces and Thermal Expansion/Contraction

FIG. 7 introduces an exemplary thermal semi conductor device 16 based oncompound materials, thermal contact between extended surfaces andthermal expansion/contraction in accordance with the invention. Thissystem presents similarities with the system presented in FIG. 4. Itconsists of two parallel plates 12 e 13 of a good conductor withinternal fins. The fins of the wall 13 are intentionally confined byfins of the wall 12, as shown in FIG. 7. The remaining space 14 isfilled with a good insulator and a gap 15 is left between fins withcorresponding apparent surfaces, filled with a compressible gas. Theappropriate system design permits the adequate thermal expansion orcontraction of the plates 12 and 13 respectively, allowing or preventingthe contact between the surfaces 11. For instance, initially thereservoir H is a relatively hotter reservoir and is positioned so thatto transfer heat to relatively colder reservoir C. In accordance withthis arrangement, lower temperatures at the wall 13 promote its thermalcontraction and higher temperatures at the wall 12 promote itsexpansion. This conjugated effect prevents the corresponding finsurfaces 11 contact keeping the good conductors away from each other,reducing the heat transfer rate of the system. On the other hand, byopposite temperature gradient, the inverse effect is expected, as shownin FIG. 8. Higher temperatures at the wall 13 promote its thermalexpansion and lower temperatures at the wall 12 promote its contraction.This conjugated effect promotes the corresponding fin surfaces 11contact allowing the contact between the good thermal conductors,increasing the heat transfer rate of the system. The great advantage ofthis system is that it can be drove exclusively by defined temperaturegradients and no external driven is necessary for its working. Thissystem automatically switches between good or poor heat transfer ratesby corresponding temperature gradients. It is also suitable for placeswith vertically displacement constraints.

While specific embodiments of the invention have been illustrated anddescribed herein, it is realized that numerous modifications,dimensions, proportions, configurations, arrangements, profiles, forms,outlines and changes for each part or for the whole invention will occurto those skilled in the art. It is therefore to be understood that theappended claims are intended to cover all such modifications and changesas fall within the true spirit and scope of the invention.

Regardless of which configuration is used, the invention can be used tocontrol the heat flux of a wide variety of substrates, including, butnot limited to, roofs, ceilings, walls, containers, tanks, pipes,trucks, boats, barges and ships.

It is important to recognize that heat transfer through anyinsulation/conduction system may include several modes: conductionthrough the solid materials; conduction or convection through the air inthe void spaces; and radiation exchange between the surfaces of thesolid matrix.

References cited

Mills, A. F. Basic Heat and Mass Transfer, Richard D. Irwin Inc.,Concord, Mass., 1995.

Hagen, K. D. Heat Transfer with Applications, Prentice-Hall, UpperSaddle River, N.J., 1999.

1. A method of conceiving an object with semi conduction heat transferproperties, the method provide a object comprising adjustable compositeslabs formed of good conductor material and good insulator materialappropriately set and adjusted enabling the unidirectional heat transferas well the control of the heat flux in presence of temperature gradient2. A heat transfer device forming a compound layer, wherein thecomposition comprises: at least a pair of parallel composite slideableslabs set in contact as one adapted for positioning at respectivelocations of differing temperature between which it is desired totransfer heat, wherein the relative longitudinal displacement betweenthe composite slabs is allowed, wherein each composite slab has at leastone segment having good thermal conductor material and one segmenthaving poor thermal conductor material alternately;
 3. A heat transferdevice forming a compound layer, wherein the composition comprises: atleast a pair of internally finned slideable parallel slabs having a goodthermal conductor material adapted for positioning at respectivelocations of differing temperature between which it is desired totransfer heat, wherein the relative longitudinal and transversaldisplacements between the slabs are allowed, wherein the empty internalspace is filled with a poor thermal conductor material allowing howeverthe relative longitudinal displacement the slabs, wherein the remainingempty internal space is filled with a compressible fluid allowing theslabs displacement and the contact between the corresponding fininternal faces, wherein a poor thermal conductor material is set betweenthe fin extremity of one slab and the internal face of the correspondingslab in order to avoid the direct contact between them;
 4. A heattransfer device forming a compound layer, wherein the compositioncomprises: at least a pair of internally finned parallel slabs having agood thermal conductor material adapted for positioning at respectivelocations of differing temperature between which it is desired totransfer heat, wherein the fins of one slab are confined by thecorresponding fins of the related slab, wherein relative longitudinalthermal expansion and contraction for the slabs is allowed, wherein theempty internal space is filled with a poor thermal conductor materialallowing however the relative longitudinal displacement the slabs,wherein the remaining empty internal space is filled with a compressiblefluid with low thermal conductivity allowing the slabs displacement andthe contact between the corresponding fin internal faces, wherein a poorthermal conductor material is set between the fin extremity of one slaband the internal face of the corresponding slab in order to avoid thedirect contact between them;
 5. A heat transfer device in accordancewith claims 1, 2, 3 and 4, wherein said good and poor thermal conductormaterial can be a liquid, a solid, a gas or a composite material;
 6. Aheat transfer device in accordance with claims 1, 2, 3 and 4, whereinsaid the contact between the corresponding fin internal surfacesestablishes a relative low thermal contact resistance.